Three-dimensional semiconductor mounting has come to be indispensable to realization of further enhance density and capacity. The three-dimensional mounting technology is a semiconductor production technology in which semiconductor chips are each thinned and they are stacked to form a multilayer structure while interconnecting them by silicon through electrodes (through silicon via (TSV)). To realize this, it is necessary to thin the substrate formed with a semiconductor circuit by grinding the non-circuit-formation surface (also called the “back side”) thereof, and to form electrodes inclusive of the TSV on the back side. Conventionally, in performing the back side grinding of a silicon substrate, a protective tape is adhered to the surface opposite to the surface to be ground, thereby to prevent the wafer from breaking during grinding. However, the protective tape uses an organic resin film as a support base material, and is insufficient in strength and heat resistance though flexible, so that the tape is unsuited to formation of the TSV or formation of a wiring layer on the back side.
Here, there has been proposed a new system which withstands the steps of grinding the back side and forming electrodes on the back side, the system involving the bonding of the semiconductor substrate to a support (of silicon, glass, or the like) with the help of an adhesive. What is most important in this new system is the adhesive to bond together the substrate and the support. This adhesive should be able to bond the substrate to the support completely without gaps remaining therein and also able to withstand this bonding step. Moreover, the adhesive should be able to permit the thin wafer to peel off easily from the support. Incidentally, the resulting adhesion layer is referred to as “temporary adhesion layer (or temporary adhesive layer)” hereinafter since it is peeled off eventually as mentioned above.
According to a known existing technology for the temporary adhesion layer and the method of its peeling, the adhesive is made from a thermofusible hydrocarbon compound and the bonding and peeling are performed while it is in a molten state with heating (see Patent Document 1, JP-A 2003-177528). Although this technology is simple and easy because it is controlled with heating alone, it becomes unstable at high temperatures above 200° C. This disadvantage limits its applications.
There has also been proposed a technology which employs a silicone pressure-sensitive adhesive for the temporary adhesive layer (see Patent Document 2, WO 2015/072418). This technology is intended to bond the substrate to the support with a silicone pressure-sensitive adhesive of addition curing type and to peel them apart by dipping them in chemicals capable of dissolving or decomposing the silicone resin. Since peeling in this way takes a very long time, it cannot be applied easily to the process for actual production.
There has been proposed another technology for peeling the adhesive layer from the support by decomposing the adhesive layer with the help of high-intensity light irradiated to the adhesive containing a light-absorbing substance (see Patent Document 3, JP-A 2013-534721). This technology has the advantage of being able to reduce the time required for treating each substrate at the time of separating the substrate from the support; however, it also has the disadvantage that the support has to be made of a metal compound for effective conversion of irradiated light into heat. The metal support is liable to cause metal contamination to the substrate.